Process for treating film



June 21, 1960 F. E. HOFFMAN 2,941,255

PRQCESS FOR TREATING FILM Filed Sept. 14, 1955 INVENTOR FRANK E. HOFFMANBY WW ATTORNEY shaft.

United States Patent() PROCESS FOR TREATING FILM Frank Edward Hoffman,Camanche, Iowa, assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Filed Sept. 14, 1955, Ser.No. 534,351

1 Claim. (Cl. 1S--57) The present invention relates to the processing oftraveling web material and more particularly to the wet processing ofregenerated cellulose film.

In the manufcature of regenerated cellulose film, viscose solution isextruded (cast) through the lips of a hopper into a tank containing acoagulating and regenerating medium. The gel film, as cast, is then ledin serpentine fashion over and under rollers through severalpurification, washing and softening tanks and finally through a dryer.The details of the process are described in US. Patent 1,548,864.

The dried film is wound on a roll and, when examined prior to coatingand slitting, may show-raised areas along its length. These raised areasmay not he very significant on a a single thickness of film but, whenwound on a roll, overlapping raised areas appear as unsightly ribbonsthroughout the length of the film. These bands, called gauge bands,cause stretching of the film in the immediate ,vicinity of the hands.When the roll is slit into narrower widths, the film strips showing theeffects of the gauge hands are discarded. This may amount to discardingas much as 20% of the film.

Attempts to minimize the loss of film due to this cause have ranged fromincreased cleaning schedules on all equipment that contact the travelingfilm (squeegees, rollers, etc.) to efforts to remove the bandsmechanically or chemically during drying. None has proved successful.

The present invention overcomes the situation in a surprisingly simplemanner. It comprises reciprocating the traveling web of gel film at anystage during wet processing, but prior to the application of a softenerto the fihn in a direction transverse to the direction of travel. For aweb of conventional width, 30-50 inches, the amount of reciprocationneed only be A to 1 /2 inches on either side of the center line of thefilm.

in the accompanying drawings, a preferred apparatus for accomplishingthe above result is disclosed.

Figure 1 is a side elevation of the apparatus.

Figure 2 is a sectional view along 2--2 of Figure 1.

Figure 3 is a sectional view along 33 of Figure 2.

The traveling film 17 is led from tank 11, after passing under roller13, over roller 15 to roller 16 and then under roller 14 in tank 12. Thefilm is reciprocated while it passes over positioning roller 16. Toaccomplish this, roller 16 is mounted on shaft 18, one end of which ispivotally held by bolt 31 between brackets 19 and 29. The brackets aremounted on a support 25'extending from one wall of tank 12. Slots 21 areprovided in the brackets to permit adjustment of the height of the Athreaded rod 22 provided with wing nuts 23 and 24, serves to set andmaintain the height of the shaft 18. The height is set so that thecenter line of the film corresponds to the center line of the machine Aice 2 and reciprocation will, occur on either side of this'center linesI i ;A plate 26 is freeto move up and down between guide brackets 20 and30. These latter brackets are mounted on a support, 27, extending from awall of tank 12. Two circular openings are out out of the plate; a loweropening 27 to receive one end of shaft 18, and an upper opening toreceive an offset shaft 28. An additional support 32 is providedadjacent the tank 12. A variable speed motor 33 is mounted on support 32and a cam 34 is mounted on the shaft of motor 33. The cam 34 cooperateswith the offset shaft or rod 28 to raise and lower the plate 26periodically as the cam rotates. This movement of the plate also raisesand lowers the shaft 18 and accompanying roller 16, thus serving toreciprocate the film 17 as it passes over roller 16. This in turn causesthe traveling film to track from side to side as it progresses throughthe washing operations, the softening treatment and the dryer. As thefilm moves from side to side, any imperfections in the film sheet tendto shift from side to side. The result is that the film, as wound on thefinal roll, has the imperfections scattered across its width rather thanpiled over a narrow area. Thus, the gauge hands are prevented. The speedof the variable speed motor is dictated by the intensity of the gaugeband problem. In general, motor speeds of Va to /5 revolution per minutehave proven satisfactory.

Although an offset shaft 28, in combination with a moveable plate 26 hasbeen shown in the drawings, it is possible for the cam and motorarrangement to act directly on shaft 18. A smooth rod over which the wetfilm will slide without scratching may be used in place of roller 16 andshaft 18. For convenience in operation, however, the illustrated designis preferred.

When the device was used in the wet processing of regenerated cellulosefilm having a width of from 30 to 50 inches with a reciprocation of A to1 inch, the number of rejected rolls (as slit) was reduced from 20.5% to3.71% of the total slit rolls. In another case where a different type ofregenerated cellulose film was being processed, the rejected rolls werereduced from 4.05% to zero. In still another case, rejects fell from6.65% when the reciprocating device was not used to 0.64% when it wasused.

The commercial advantages are immediately obvious. The amount of filmthat formerly had to be discarded is reduced at least five-fold. Thedevice for accomplishing this result is simple to install, requireslittle maintenance and is easily adjustable. It is believed that thedevice will be useful wherever traveling webs of film such asregenerated cellulose, cellulose acetate, polyethylene, polyesters, etc.must be processed with liquids in a continuous manner.

As many different embodiments may he made without departing form thespirit and scope of this invention,

it is understood that the invention is not limited except (References onfollowing page) l ,9 ,205 References Cited in the file of this patent2,476,070 UNITED STATES PATENTS $32 32? Marshall June 15, 1909 Hill"Iune 29, 1926" 5 Davis Sept 13, 193s- 385,783 1,062,707

Solliday July 12, 1949 Smith'et a1. Jan. 11, 1955 Russell Mar. 29, 1955FOREIGN PATENTS Great Britain Jan. 5, 1933 France Apr. 27, 1954

